Kuiri Manabendra, Kumar Chandan, Chakraborty Biswanath, Gupta Satyendra N, Naik Mit H, Jain Manish, Sood A K, Das Anindya
Nanotechnology. 2015 Dec 4;26(48):485704. doi: 10.1088/0957-4484/26/48/485704. Epub 2015 Nov 12.
Two-dimensional materials and their heterostructures have emerged as a new class of materials, not only for fundamental physics but also for electronic and optoelectronic applications. Black phosphorus (BP) is a relatively new addition to this class of materials. Its strong in-plane anisotropy makes BP a unique material for making conceptually new types of electronic devices. However, the global density of states (DOS) of BP in device geometry has not been measured experimentally. Here, we report the quantum capacitance measurements together with the conductance measurements on an hBN-protected few-layer BP (∼six layers) in a dual-gated field effect transistor (FET) geometry. The measured DOS from our quantum capacitance is compared with density functional theory (DFT). Our results reveal that the transport gap for quantum capacitance is smaller than that in conductance measurements due to the presence of localized states near the band edge. The presence of localized states is confirmed by the variable range hopping seen in our temperature dependence conductivity. A large asymmetry is observed between the electron and hole side. This asymmetric nature is attributed to the anisotropic band dispersion of BP. Our measurements establish the uniqueness of quantum capacitance in probing the localized states near the band edge, hitherto not seen in conductance measurements.
二维材料及其异质结构已成为一类新型材料，不仅在基础物理学领域，而且在电子和光电子应用方面都有重要价值。黑磷（BP）是这类材料中的新成员。其强烈的面内各向异性使黑磷成为制造概念上新型电子器件的独特材料。然而，器件几何结构中黑磷的全局态密度（DOS）尚未通过实验测量。在此，我们报告了在双栅场效应晶体管（FET）几何结构中对hBN保护的几层（约六层）BP进行量子电容测量以及电导测量的结果。将我们通过量子电容测量得到的DOS与密度泛函理论（DFT）进行了比较。我们的结果表明，由于带边附近存在局域态，量子电容的输运能隙小于电导测量中的能隙。我们在温度依赖电导率中观察到的变程跳跃证实了局域态的存在。在电子和空穴侧观察到很大的不对称性。这种不对称性质归因于黑磷的各向异性能带色散。我们的测量确立了量子电容在探测带边附近局域态方面的独特性，这在电导测量中迄今尚未见到。
